The purpose of this work is to determine how tissue specific regulation is accomplished for a particular gene in Drosophila melanogaster. This goal will be approached by studying the activity of the normally functioning gene and mutants of the gene that affect specific tissues. Cloned DNA segments will be used to study the structure of normal and mutant genes and the RNA products of these genes. I hope to understand how a newly recognized class of mutators, mobile DNA elements, disrupt the activity of the gene in question. These mobile elements are apparently present in many types of organisms, and Drosophila offers an opportunity to understand what effects the elements may have on a gene's activity.